Difference between revisions of "Part:BBa K1080011"

Revision as of 09:57, 17 October 2014

ChlI2
Magnesium chelatase subunit I - The second gene which catalyzes the insertion of magnesium ion into protoporphyrin IX to yield Mg-protoporphyrin IX. Forms an ATP dependent hexameric ring complex and a complex with the ChlD subunit.

Usage and Biology

The chelation of magnesium in protoporphyrin IX is dependant on several genes. These include ChlI, ChlD, ChlH and GUN4. According to previous research, the ChlI component of this pathway proves essential in the chelation of magnesium. The ChlI gene encodes 2 isoforms, ChlI1 and ChlI2. The already familiar function of ChlI1 is well known and documented. The second isoform, ChlI2 is also integral in magnesium chelation complementing ChlI1 [http://www.plantphysiol.org/content/150/2/636.full]

Figure 1: Reaction catalysed by Mg-chelatase, inserting a magnesium ion into Protoporphyrin IX to make Mg-protoporphyrin IX.

Reaction: ATP + protoporphyrin IX + Mg2+ + H2O = ADP + phosphate + Mg-protoporphyrin IX + 2 H+.

Operon usage

Figure 2: This gene has been used in an operon with other genes responsible for the synthesis pathway from Protoporphyrin IX to MG-protoporphyrin IX. ChlI1 and ChlD form an Mg-chelatase complex, which acts upon protoporphyrin, catalysing the insertion of a Magnesium ion into the centre of the protoporphyrin IX. GUN4 aids this reaction by activating the Mg-chelatase enzyme complex.
The plasmid is under the control of the lac promoter.
The entire operon can be found at BBa_K1326008.
Future plans involve adding ChlH to this operon, which binds Mg-chelatase with GUN4 to protoporphyrin.

ChlI structure

Figure 3: ChlI protein crystal structure.


Sequence and Features

Amino Acid Sequence

MPSTKAAKKP NFPFVKIQGQ EEMKLALLLN VVDPNIGGVL IMGDRGTAKS VAVRALVDML
PDIDVVEGDA FNSSPTDPKF MGPDTLQRFR NGEKLPTVRM RTPLVELPLG ATEDRICGTI
DIEKALTQGI KAYEPGLLAK ANRGILYVDE VNLLDDGLVD VVLDSSASGL NTVEREGVSI
VHPARFIMIG SGNPQEGELR PQLLDRFGMS VNVATLQDTK QRTQLVLDRL AYEADPDAFV
DSCKAEQTAL TDKLEAARQR LRSVKISEEL QILISDICSR LDVDGLRGDI VINRAAKALV
AFEGRTEVTT NDVERVISGC LNHRLRKDPL DPIDNGTKVA ILFKRMTDPE IMKREEEAKK

Please note the modified algorithm for extinction coefficient.

Number of amino acids: 393

Molecular weight: 42954.3

Theoretical pI: 5.78

Amino acid composition:
Ala (A) 38 9.7%
Arg (R) 30 7.6%
Asn (N) 14 3.6%
Asp (D) 32 8.1%
Cys (C) 4 1.0%
Gln (Q) 12 3.1%
Glu (E) 28 7.1%
Gly (G) 29 7.4%
His (H) 2 0.5%
Ile (I) 22 5.6%
Leu (L) 41 10.4%
Lys (K) 27 6.9%
Met (M) 10 2.5%
Phe (F) 10 2.5%
Pro (P) 22 5.6%
Ser (S) 16 4.1%
Thr (T) 21 5.3%
Trp (W) 1 0.3%
Tyr (Y) 3 0.8%
Val (V) 31 7.9%
Pyl (O) 0 0.0%
Sec (U) 0 0.0%

(B)   0	  0.0%
(Z)   0	  0.0%
(X)   0	  0.0%

Total number of negatively charged residues (Asp + Glu): 60 Total number of positively charged residues (Arg + Lys): 57

Atomic composition:

Carbon C 1875 Hydrogen H 3103 Nitrogen N 541 Oxygen O 580 Sulfur S 14

Formula: C1875H3103N541O580S14 Total number of atoms: 6113

Extinction coefficients:

Extinction coefficients are in units of M-1 cm-1, at 280 nm measured in water.

Ext. coefficient 10220 Abs 0.1% (=1 g/l) 0.238, assuming all pairs of Cys residues form cystines

Ext. coefficient 9970 Abs 0.1% (=1 g/l) 0.232, assuming all Cys residues are reduced

Estimated half-life:

The N-terminal of the sequence considered is M (Met).

The estimated half-life is:

                            30 hours (mammalian reticulocytes, in vitro).
                           >20 hours (yeast, in vivo).
                           >10 hours (Escherichia coli, in vivo).

Instability index:

The instability index (II) is computed to be 32.87 This classifies the protein as stable.

Aliphatic index: 95.06

Grand average of hydropathicity (GRAVY): -0.296

Source

Chlamydomonas reinhardtii